WO2021066265A1

WO2021066265A1 - Very low-sulfur fuel oil and method for producing the same

Info

Publication number: WO2021066265A1
Application number: PCT/KR2020/003307
Authority: WO
Inventors: Haewon JUNG; Cheolhyun KIM; Woongchul SHIN
Original assignee: Hyundai Oilbank Co., Ltd.
Priority date: 2019-10-02
Filing date: 2020-03-10
Publication date: 2021-04-08
Also published as: KR20210157454A; US20220403256A1; KR20210039743A

Abstract

The present invention relates to a method for producing very low-sulfur fuel oil having high compatibility and high stability, comprising: mixing petroleum residua obtained from at least two different petroleum refining processes, adding a hydrocarbon solvent to the residual petroleum mixture, heating the mixture of the petroleum residua mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions and the hydrocarbon solvent from the mixture of the petroleum residua mixture and hydrocarbon solvent with raffinate having asphaltenes therein being left, and removing the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil, wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt% or less based on the total weight of the very low-sulfur fuel oil, and very low-sulfur fuel oil produced by the production method.

Description

VERY LOW-SULFUR FUEL OIL AND METHOD FOR PRODUCING THE SAME

The present invention relates to a method for producing a very low-sulfur oil having a sulfur content of 0.5 wt% or less, comprising steps of mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils like gasoline, heavy oil, jet aircraft fuel, etc. to obtain a petroleum residua mixture; adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture with asphaltenes eliminated and the hydrocarbon solvent; heating mixture of the petroleum residua mixture and the hydrocarbon solvent to extract and recover a mixture of oil fractions from the petroleum residua mixture and the hydrocarbon solvent with raffinate having asphaltenes therein being left, and recovering the hydrocarbon solvent from extract stream: and a very low-sulfur fuel oil, particularly marine fuel oil, produced by the above method.

As International Marine Organization (IMO) regulation on the sulfur content of marine fuel oil will come into effect from 2020, the oil refining industry has entered a new phase of marine fuel oil production. As the regulation standard on the sulfur content of marine fuel oil is greatly strengthened from the existing sulfur content of 3.5 wt% to a sulfur content of 0.5 wt%, additional desulfurization treatment of existing marine fuel oil products has become essential.

The relevant literature presents low asphaltene content and high aromatics content as recommendations for ensuring the stability of marine fuel oil. It has been known that incompatibility of oil blend increases due to aggregation of asphaltenes therein, when oils produced by different processes (e.g., straight-run fuel oil and cracked oil) or oils having greatly different viscosities and densities (e.g., FCC (Fluidized Catalytic Cracker) slurry oil and diesel oil) are mixed together to balance physical properties. In the case of an oil containing large amounts of saturated hydrocarbon compounds and asphaltenes, asphaltenes are not completely dispersed in the form of micelles therein due to relatively small amounts of aromatic compounds thereof and thus, aggregation and precipitation of asphaltenes occur as time goes by. The oil produced by a single process is in general regarded to have low stability, as described above. Even in the case of a certain oil having a sufficient stability on its own, the tendency to form impurities such as sludge and precipitate may be accelerated in oil blend, resulting in insufficient incompatibility thereof, when it is blended with the other oil derived from other refining processes.

As the regulations on sulfur content have been greatly strengthened as introduced above, it has become difficult to produce products with price competitiveness using oil produced in a single process, such as existing marine fuel oil, and it can be considered that most products are produced by mixing very low-sulfur oil with existing high-sulfur oil. In addition, as the margin of oil refinery complex continues to be lowered, many oil refiners are tend to increase the input of low-quality crude oil, which is high in acidity and contains excessive amounts of impurities such as sulfur, nitrogen, and metals, but has low prices. As this tendency is intensified, the quality of marine fuel oil using residuum oil as a raw material may be degraded. Accordingly, the proportion of very low-sulfur oil such as ultra-low sulfur diesel that have been blended in little amounts in high sulfur fuel oil has to be increased rapidly to satisfy a sulfur content specification, and in some cases, it can be attempted to mix different residuum oils produced by two or more upgrading or cracking processes. These attempts can have a significant defect on the stability of the oil as mentioned above.

Many analysis methods have been proposed as methods for measuring the stability and compatibility of oils. Among these methods, one of methods that enable eidetic determination is Spot Test (ASTM D4740). The rating for the Spot Test is shown in FIG. 1. The rating for the Spot Test is referred to as Spot Rating and can be rated from 1 to 5.

In the case of an oil containing large amounts of saturate and asphaltenes, even if it is not mixed with other oil, the spot rating may worsen as the contents of solids and sludge increase due to the aggregation of asphaltenes over time. In the case of oil blend obtained by mixing oils originated from different upgrading or cracking processes, the spot rating changes can be observed more immediately than in the case of single oils. An oil showing spot rating of 3 or higher is very unstable, and thus when it is stored in a marine oil tanker for a long period of time, additional deterioration in the stability of the oil is inevitable, and in this case, normal operation of the purifier and engine in the marine fuel system is severely affected. The production of stable marine fuel oils using residuum oil as a raw material can be achieved through an additional limited process (vacuum residuum desulfurization (VRDS)) using a production facility, which is very advanced and requires excessive operating costs (due to the use of excessive hydrogen). However, this production process is not profitable due to huge CAPEX, OPEX, and restricted types of feed oil. In the situation where a huge amount of high-sulfur fuel oil, which has been used on all international waters, has to be replaced by very low-sulfur fuel oil, if this very low-sulfur fuel oil is produced only through the limited process, it will difficult to sufficiently meet the demand for the very low-sulfur fuel oil, and the very low-sulfur fuel oil produced through this production will be disadvantageous in terms of price competitiveness.

The present invention has been made in order to overcome the above-described stability and compatibility problems in prior arts and disadvantages occurring when a plurality of different oil-fractions are mixed together, and it is an object of the present invention to provide a method for producing very low-sulfur fuel oil (VLSFO), which uses a relatively simple production process, does not require much investment in the process, may use, as a raw material, oil-fractions from various upstream processes, particularly petroleum residua remaining after production of relatively high quality fuel oil fractions and may also drastically reduce the production cost. That is, an object of the present invention is to provide VLSFO having high stability (spot rating of 1) using, as a raw material, petroleum residua produced in oil refining processes, which may be used for the production of marine fuel oil, and a mixture of petroleum residua mixed at a predetermined ratio.

The present invention provides a method for producing very low-sulfur fuel oil, comprising steps of:

mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture;

adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture with asphaltenes eliminated and the hydrocarbon solvent;

heating the mixture of the petroleum residua mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions from the petroleum residua mixture and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and

recovering the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil,

wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt% or less based on the total weight of the very low-sulfur fuel oil.

The petroleum residua may be selected from the group consisting of atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DAO), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), t-VGO (hydrotreated VGO), high-sulfur diesel (HSD), and ultra-low-sulfur diesel (ULSD).

The hydrocarbon solvent may preferably be selected C ₃-C ₅ hydrocarbon solvent or a mixture of two or more thereof. The C ₃-C ₅ hydrocarbon solvent may preferably be selected from the group consisting of n-propane, n-butane, i-butane, n-pentane, i-pentane, and a mixture of two or more thereof, and may more preferably be selected from the group consisting of n-pentane, i-pentane, and a mixture thereof. Most preferably, the C ₃-C ₅ hydrocarbon solvent may be n-pentane.

The hydrocarbon solvent is added with the volume ratio of 1 to 4 : 1 of the hydrocarbon solvent to the petroleum residua mixture in an extraction column at a pressure ranging from 30 to 50 barg (gauge pressure) and a temperature ranging from 100 to 230℃.

The mixture of the petroleum residua mixture and hydrocarbon solvent is heated to extract and recover a mixture of oil fractions and the hydrocarbon solvent with raffinate having asphaltenes therein being left.

A very low-sulfur fuel oil according to the present invention may be obtained by mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture; adding C ₃-C ₅ hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent, heating the mixture of the petroleum residua mixture and the hydrocarbon solvent to extract and recover a mixture of oil fractions and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and recovering the hydrocarbon solvent from the extract stream. The very low-sulfur fuel oil of the present invention may have a sulfur content of 0.5 wt% or less based on the total weight of the very low-sulfur fuel oil, and an asphaltene content of 0.1 to 0.6 wt%, more preferably 0.05 to 0.55 wt%, most preferably 0.01 to 0.50 wt%, based on the total weight of the very low-sulfur fuel oil.

According to the present invention, very low-sulfur fuel oil having high compatibility and high stability may be produced using, as a raw material, a mixture of petroleum residua obtained from at least two different petroleum refining processes as a substance remaining after production of relatively high quality fuel oil fractions, and the mixing ratio between the petroleum residua may be selected flexibly in consideration of the operating status of petroleum refining processes. In addition, the production cost may be significantly reduced compared to that of upgrading process such as hydro-desulfurization process, which use limited feedstocks and require high operating costs.

As demonstration of such effects, the very low-sulfur fuel oil (VLSFO) produced by the present invention shows a difference in behavior and stability from conventional marine fuel oil when it is introduced into a purifier and engine in a ship. This difference is analyzed to be due to the change of components (mainly saturates, aromatics, resins and asphaltenes) that are inevitably contained in oil fractions.

FIG. 1 is photographs showing the spot rating of a spot test (ASTM D4740) for evaluating the stability of fuel oil.

FIG. 2 is a flowchart showing a production process of very low sulfur-fuel oil by separating and removing asphaltenes from a petroleum residua mixture according to the present invention.

A method of very low-sulfur fuel oil according to the present invention comprises steps of:

adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent;

heating the mixture of the petroleum residua mixture and the hydrocarbon solvent to extract and recover a mixture of oil fractions and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and

recovering the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil, wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt% or less based on the total weight of the very low-sulfur fuel oil.

The petroleum residua may be selected from the group consisting of atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DAO), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), hydrotreated vacuum gas oil(t-VGO), high-sulfur diesel (HSD), and ultra-low-sulfur diesel (ULSD).

In the present specification, the term "high-quality oils" refers to oils such as jet aircraft oil and gasoline, which have low boiling points and high economic values, and the expression "petroleum residuum" as used in the present invention refers to an oil fraction, which is obtained from a petroleum refining process for production of relatively high quality fuel oil fractions, mainly in the form of residuum, and have a high sulfur and asphaltene content.

Specifically, according to the present invention, very low-sulfur fuel oil may be produced by adding a C ₃-C ₅ hydrocarbon solvent to a mixture obtained by mixing different kinds of petroleum residua at a predetermined ratio and separating asphaltenes, which is a source material that causes aggregation and precipitation, from the mixture of petroleum residua. The C ₃-C ₅ hydrocarbon solvent may preferably be selected from the group consisting of n-propane, n-butane, i-butane, n-pentane, i-pentane, and a mixture of two or more thereof, may more preferably be selected from the group consisting of n-pentane. i-pentane, and a mixture thereof, most preferably n-pentane.

For separation of asphaltenes in an extraction column, the ratio of the C ₃-C ₅ hydrocarbon solvent to the petroleum residua mixture is 1 to 4 : 1, more preferably 2 to 3: 1, the pressure that is used for the separation is 30 to 50 barg, more preferably 35 to 46 barg, most preferably 38 to 43 barg, and the temperature that is used for the separation may be T _c(critical temperature of the hydrocarbon solvent) minus 20℃ to T _c plus 20℃, more preferably T _c-15℃ to T _c+15℃, most preferably T _c-10℃ to T _c+10℃. The temperature may range from 100℃ to 230℃.

After separation of the asphaltenes, the hydrocarbon solvent is removed from the extract stream, thereby obtaining very low-sulfur fuel oil. The recovered hydrocarbon solvent may be reused, and a stream of raffinate may be used as a blending stock for conventional coker unit.

Through several repeated experiments, the present inventors have found that hydrocarbon solvents exhibit a stronger solvent effect as the number of carbon atoms in the hydrocarbon solvents increases, but when a hydrocarbon solvent having a high solvent effect, such as hexane having 6 carbon atoms, is used, the efficiency of removal of asphaltenes from the petroleum residua mixture is greatly reduced, and in the case of hydrocarbon solvents having the same carbon number, a linear hydrocarbon (e.g., n-pentane) exhibits a stronger solvent effect than a branched hydrocarbon (e.g., i-pentane). In addition, the present inventors have found that the yield of VLSFO increases at low temperature and high pressure depending on the density change and thermodynamic preference of the supercritical hydrocarbon solvent in the extraction column in which the extraction of oil fractions is performed. The present inventors have found that a proper hydrocarbon solvent needs to be used to maximize the yield of VLSFO while preventing the loss of oil fractions, and in particular, have found that it is necessary to select a suitable hydrocarbon solvent to increase the stability of the mixture of oil fractions.

The very low-sulfur fuel of the present invention may have a sulfur content of 0.001 to 0.5 wt%, preferably 0.05 to 0.49 wt%, most preferably 0.1 to 0.48 wt%, based on the total weight of the very low-sulfur fuel.

The very low-sulfur fuel according to the present invention produced from the mixture of petroleum residua exhibits improved storage stability.

That is, the petroleum residuum have a high content of saturates and/or a high content of asphaltene, and hence when this petroleum residuum are used as a raw material to produce fuel oil, the stability of the fuel oil is low. However, according to the present invention, when two or more petroleum residua selected from among atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DAO), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), t-VGO (hydrotreated VGO (vacuum gas oil), high-sulfur diesel (HSD), and ultra-low-sulfur diesel (ULSD) are mixed together at a predetermined ratio and the mixture is treated with a hydrocarbon solvent to remove asphaltenes, very low-sulfur fuel oil having high stability and meets specifications on the very low-sulfur fuel oil.

Hereinafter, the present invention will be described in detail with reference to examples.

[Example 1]

In an extraction column, 1,457,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1 : 1, was mixed with n-pentane solvent at a solvent/petroleum residua mixture volume ratio of 2 under conditions of 42 barg and 205℃, and extracted for 60 minutes (extraction column residence time). Total extraction process operation time was 660 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 1,394,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below. The sulfur content was measured in accordance with ASTM D4294, and the asphaltene content was measured in accordance with ASTM D6560.

[Example 2]

In an extraction column, 1,643,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1 : 1, was mixed with n-pentane solvent at a solvent/ petroleum residua mixture volume ratio of 2 under conditions of 42 barg and 185℃, and extracted for 40 minutes (extraction column residence time). Total extraction process operation time was 480 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 1,615,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below.

[Example 3]

In an extraction column, 1,325,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1 : 1, was mixed with i-pentane solvent at a solvent/ petroleum residua mixture volume ratio of 1 under conditions of 42 barg and 220℃, and extracted for 90 minutes (extraction column residence time). Total extraction process operation time was 600 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 958,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below.

[Example 4]

In an extraction column, 1,656,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1 : 1, was mixed with an n-pentane solvent at a solvent/ petroleum residua mixture volume ratio of 1 under conditions of 42 barg and 220℃, and extracted for 70 minutes (extraction column residence time). Total extraction process operation time was 600 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 1,495,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below.

[Comparative Example 1]

In an extraction column, 1,325,000 liter of t-AR as single petroleum residuum instead of petroleum residua mixture was mixed with an n-pentane solvent at a solvent/petroleum residuum volume ratio of 3 under conditions of 42 barg and 190℃, and extracted for 70 minutes (extraction column residence time). Total extraction process operation time was 600 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fraction from the petroleum residuum and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of the oil fraction and the solvent, thereby obtaining 1,176,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 2 below.

[Comparative Example 2]

Low-sulfur AR without removing asphaltenes was measured for its sulfur content, asphaltene content and spot rating by a spot test, and the results of the measurement are shown in Table 2 below. Here, the low-sulfur AR was an unhydrotreated atmospheric residuum having low sulfur content.

[Comparative Example 3]

A mixture of petroleum residua, obtained by mixing low-sulfur AR and ULSD at a volume ratio of 91 : 9, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 2 below.

[Comparative Example 4]

A mixture of petroleum residua, obtained by mixing low-sulfur AR and ULSD at a volume ratio of 76 : 24, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 2 below.

[Comparative Example 5]

A mixture of petroleum residua, obtained by mixing AR, ULSD and UCOl at a volume ratio of 91 : 4.5 : 4.5, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 3 below.

[Comparative Example 6]

A mixture of petroleum residua, obtained by mixing AR, ULSD and SLO at a volume ratio of 72 : 20 : 8, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 3 below. Here, the SLO was residuum in a fluidized catalytic cracking (FCC) process.

[Comparative Example 7]

A mixture of petroleum residua, obtained by mixing t-AR, LCO, SLO and H-Aro at a volume ratio of 80 : 9 : 6 : 5, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 3 below. Here, the LCO was a kind of low-price oil fraction produced in a fluidized catalytic cracking process, and the H-Aro was a by-product in an aromatic production process.

		Example 1		Example 2		Example 3		Example 4
Petroleum residuum		t-AR	t-DAO	t-AR	t-DAO	t-AR	t-DAO	t-AR	t-DAO
Petroleum residuum	S% (wt%)	0.65	0.27	0.65	0.25	0.7	0.23	0.72	0.2
	As% (wt%)	3.21	0.1	3.12	0.1	3.08	0.05	3.25	0.06
	S.R. (1-5)	4	1	4	1	4	1	4	1
Mixing ratio (v/v)		50	50	50	50	50	50	50	50
Petroleum residua mixture (before treatment with solvent)	S% (wt%)	0.48		0.46		0.47		0.47
	As% (wt%)	1.51		1.56		1.39		1.53
	S.R. (1-5)	3		3		4		3
Solvent/petroleum residuum (v/v)		2		2		1		1
Solvent		n-pentane		n-pentane		i-pentane		n-pentane
Process conditions (barg/℃)		42/205		42/185		42/220		42/220
Oil fraction (after treatment with solvent)	S% (wt%)	0.48		0.47		0.46		0.46
	As% (wt%)	0.24		0.60		0.16		0.57
	S.R. (1-5)	1		1		1		1
Storage stability (days)		30+		30+		30+		30+
Yield (%)		96		98		72		90

		Comp. Example 1	Comp. Example 2	Comp. Example 3		Comp. Example 4
Petroleum residuum		t-AR	LSAR	LSAR	USLD	LSAR	USLD
Petroleum residuum	S% (wt%)	0.67	0.48	0.53	<0.001	0.58	<0.001
	As% (wt%)	4.03	0.51	0.53	<0.01	0.51	<0.01
	S.R. (1-5)	4	1	1	1	1	1
Mixing ratio (v/v)		-	-	91	9	76	24
Petroleum residua mixture (before treatment with solvent)	S% (wt%)	-	-	0.48		0.45
	As% (wt%)	-	-	0.48		0.4
	S.R. (1-5)	-	-	1		2
Solvent/petroleum residuum (v/v)		3	-	-		-
Solvent		n-pentane	-	-		-
Process conditions (barg/℃)		42/190
Oil fraction (after treatment with solvent)	S% (wt%)	0.65
	As% (wt%)	0.26
	S.R. (1-5)	1
Storage stability (days)		30+	14-18	14-18		14-18
Yield (%)		89	-	-		-

		Comp. Example 5			Comp. Example 6			Comp. Example 7
Petroleum residuum		LSAR	USLD	UCO	LSAR	USLD	LSO	t-AR	LCO	SLO	H-Aro
Petroleum residuum	S% (wt%)	0.55	<0.001	<0.001	0.56	<0.001	1.15	0.45	0.67	1.12	<0.001
	As% (wt%)	0.55	<0.01	<0.01	0.52	<0.01	3.52	3.48	<0.01	3.45	<0.01
	S.R. (1-5)	1	1	1	1	1	1	4	1	1	1
Mixing ratio (v/v)		91	4.5	4.5	72	20	8	80	9	6	5
Petroleum residua mixture (before treatment with solvent)	S% (wt%)	0.49			0.5			0.48
	As% (wt%)	0.51			0.68			3.04
	S.R. (1-5)	2			3			4
Solvent/petroleum residuum (v/v)		-			-			-
Solvent		-			-			-
Process conditions (barg/℃)		-			-			-
Oil fraction (after treatment with solvent)	S% (wt%)	-			-			-
	As% (wt%)	-			-			-
	S.R. (1-5)	-			-			-
Storage stability (days)		14-18			i			i
Yield (%)		-			-			-

In Tables 1 to 3 above, S% denotes sulfur content, As% denotes asphaltene content, and S.R. denotes spot rating. In Table 3 above, "i" denotes immediately after mixing, and indicates that storage stability was not determined due to high spot rating immediately after mixing.

Based on the results shown in Tables 1 to 3 above, the effects of the present invention will be described hereinbelow.

1. It could be confirmed that the Examples, in which asphaltene was removed from the petroleum residua mixture, all exhibited high stability after asphaltene removal from low stability before asphaltene removal, suggesting that these Examples demonstrate the stability of the oil fraction according to the present invention. In addition, it could be confirmed that, in the storage stability of the oil fraction, due to removal of asphaltene, the Examples showed a spot rating of 1 without time-dependent changes even after 30 days, suggesting that the storage stability of the oil fraction was also greatly improved.

2. It could be confirmed that Example 1, in which asphaltene was removed from the mixture of two petroleum residua, exhibited the stability and storage stability comparable to Comparative Example 1, in which asphaltene was removed from a single petroleum residuum. In addition, it could be confirmed that the yield of Example 1 was higher than that of Comparative Example 1 with a reduced solvent amount and elevated process temperature compared to Comparative Example 1.

3. When comparing Examples 1 and 2, in which asphaltene was removed from the same petroleum residua mixture and the same solvent was used in the same amount, it could be confirmed that the yield was improved by lowering the process temperature. This suggests that the yield may vary depending on the density of the supercritical solvent in the extraction column.

4. When comparing Examples 3 and 4, in which asphaltene was removed from petroleum residua mixture and the solvent was used in the same amount, it could be confirmed that the yield of Example 4, in which n-pentane was used, was greatly improved compared to that of Example 3 in which i-pentane was used. This also suggests that the yield may vary depending on presence of branching in the solvent and the density of the supercritical solvent in the extraction column.

5. Comparative Examples 2 and 3, in which asphaltene was not removed, showed a spot rating of 1 immediately after mixing, and thus exhibited stability, but the spot rating was degraded to 2 after 14 to 18 days of storage after mixing.

6. Comparative Examples 4 and 5, in which asphaltene was not removed, showed a spot rating of 2 immediately after mixing, but the spot rating was degraded to 3 after 14 to 18 days of storage after mixing. Thus, it could be confirmed that the Comparative Examples (Comparative Examples 2 to 5), which showed high stability immediately after mixing, showed deterioration in storage stability.

7. The petroleum residua mixtures of Examples 6 and 7, from which asphaltene was not removed and which included the petroleum residuum having a high asphaltene content, showed low stability even immediately after mixing.

Although only the petroleum residua mixture comprising t-AR and t-DAO was described in the above Examples, similar results could also be obtained for other mixture of petroleum residua, as listed above, remaining after producing high-quality oils.

While the present invention has been described above with reference to the specific embodiments, it is to be understood that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited by the described embodiments, but should be defined not only by the appended claims, but also by the equivalents of the claims.

Claims

A method for producing very low-sulfur fuel oil, comprising steps of:

mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture;

adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent;

heating of the mixture of the residual petroleum mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions from the petroleum residua mixture and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and

removing the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil;

wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt% or less based on the total weight of the very low-sulfur fuel oil.
The method of claim 1, wherein the petroleum residua are selected from the group consisting of atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DAO), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), t-VGO (hydrotreated VGO vacuum gas oil), high-sulfur diesel (HSD), and ultra-low-sulfur diesel(ULSD).
The method of claim 1, wherein the hydrocarbon solvent is C ₃-C ₅ hydrocarbon solvent or a mixture of two or more thereof.
The method of claim 3, wherein the C ₃-C ₅ hydrocarbon solvent is selected from the group consisting of n-propane, n-butane, i-butane, n-pentane, and i-pentane.
The method of claim 1, wherein the hydrocarbon solvent is added with the volume ratio of 1 to 4 : 1 of the hydrocarbon solvent to the petroleum residua mixture in an extraction column at a pressure ranging from 30 to 50 barg and a temperature ranging from 100℃ to 230℃.
Very low-sulfur fuel oil which is obtained by a method for producing very low-sulfur fuel oil, comprising steps of:

mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture;

adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent;

heating of the mixture of the residual petroleum mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions from the petroleum residua mixture and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and

removing the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil,

wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt% or less based on the total weight of the very low-sulfur fuel oil.
The very low-sulfur fuel oil of claim 6, wherein the petroleum residua are selected from the group consisting of AR, VR, t-AR, t-VR, DAO, t-DAO, UCO, VGO, t-VGO, HSD, and ULSD.
The very low-sulfur fuel oil of claim 6, having an asphaltene content of 0.01 to 0.6 wt% based on the total weight of the very low-sulfur fuel oil.
The very low-sulfur fuel oil of claim 6, wherein the hydrocarbon solvent is C ₃-C ₅ hydrocarbon solvent or a mixture of two or more thereof.